The present application claims priority under 35 U.S.,C. xc2xa7119 of German Patent Application No. 199 02 623.8, filed on Jan. 23, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a headbox of a paper machine having at least one material suspension supplying system, at least one subsequent region for producing turbulence, and one headbox nozzle having one first and one second dividing wall running the width of the machine. The headbox nozzle has a first path in which the total cross-section of the headbox nozzle, i.e., total free cross-sectional surface flowed through by suspension, steadily and continuously decreases such that a second, shorter path immediately follows the first path.
2. Discussion of Background Information
A headbox similar in general to the above-noted headbox is disclosed in commonly assigned U.S. Pat. No. 5,599,428. In this patent, different variations of multi-layer headboxes, which are provided with differently constructed or formed separating lamellas, are disclosed.
Paper manufactured using headboxes of the above-noted type has the problem of insufficient crosswise stiffness SCTcross, which can cause disruptions in operation when used, e.g., in modem copying systems or in printers with automatic paper feed. Further, it would be advantageous for a breaking length ratio L/Q, where L is lengthwise in a machine direction and Q is crosswise to the machine direction, after sheet formation to be reduced to a range of between approximately 0,6 and 1.0, if possible.
The present invention provides a headbox that improves the crosswise stiffness of manufactured paper in which breaking length ration L/Q can be reduced, if possible.
The inventors of the instant invention recognize that the crosswise stiffness of the paper improves substantially if care is taken, by appropriately shaping the headbox nozzles, especially in the end region, to ensure that the fibers in the material suspension in the end region of the nozzle are turned more strongly in the z direction lying parallel to the sheet surface and, if possible, stretched as well.
Accordingly, the instant invention is directed to headbox of a paper machine with at least one material suspension supplying system, at least one following region for producing turbulence, and one headbox nozzle with one first and one second dividing wall running the width of the machine. The headbox nozzle has a first path in which a total cross-section of the headbox nozzle, i.e., the total free cross-sectional surface flowed through by the suspension in the respective machine section, steadily and continually decreases, and a second, shorter path immediately following the first path. Further, the second path has a continually widening total cross-section that extends toward an end of the headbox nozzle, which causes a flow deceleration in the end region of the headbox nozzle so that no substantial turbulence arises. The speed profile hereby caused stretches fibers in the suspension in the z direction and improves the crosswise stiffness of the finished paper. An additional positive side effect of this influence on the suspension is that the breaking length ratio L/Q decreases and can take on values between approximately 0.6 and 1.0.
According to an exemplary embodiment of the invention, an additional third path, which directly follows the second path, can be positioned to extend to the end of the headbox nozzle. In this manner, the second path has a continually widening total cross-section and the third path can have a steadily and constantly decreasing total cross-section. It may be advantageous for the length of the third path to be shorter than the length of the second path, and for the length of the second path to be shorter than the length of the first path. By selecting the corresponding ratios of the path length, it is possible to increase or decrease the crosswise stiffness stimulating effect. As such, the length of the third path should remain shorter than the length of the second path. This length ratio prevents the fiber orientation achieved in the second path from being overcompensated in the third path.
The first path can be positioned to begin immediately downstream of the turbulence producing region. Further, the total cross-section of the headbox nozzle can be formed, at least across one part of the headbox nozzle, by only one suspension conduit. In this way, no separation elements for separating individual levels are present in this region. This arrangement can reduce edge effects, and the height of the flow cross-section available at one unit can correspond to the total cross-section, so that a better fiber orientation in the z direction can be achieved.
For example, when the headbox is employed as a multiple layer headbox, it can be advantageous for the total cross-section of the headbox nozzle to include several suspension conduits, at least over a part of the headbox nozzle length, which are formed, e.g., by at least one separating element that extends across width of the machine and that is arranged between the first and second dividing walls. Moreover, it can be particularly advantageous for all suspension conduits to have the same cross-section progression without exception so that the same acceleration and deceleration ratios are provided for the suspension flowing through each conduit. It may also be advantageous for all suspension conduits without exception to have a congruent form, and be symmetrically congruent. Not only does this allow even progression of the acceleration and deceleration in the suspension conduits, but it also allows the vector field in each suspension conduit to be identical along the entire length.
In another exemplary embodiment, the degree of divergence in the region of the second path can be the same for all suspension conduits.
For example, when utilizing internal separating elements, the divergence of the individual suspension conduits can be achieved in that the separating elements in the region of the second path are arranged to have a taper. Here, it can be advantageous for the degree of convergence of the surfaces of the tapering ends of all separating elements to be the same so as to achieve as unified a flow ratio as possible across the cross-section of the headbox.
It may be further advantageous for the progression of the upper wall and/or lower wall, at least in the second region, to be constructed or formed symmetrically to the progression of the surface of the neighboring separation element. In this manner, the outermost suspension conduits can be constructed as identically to the innermost suspension conduits as possible.
Further, the headbox according to the present invention includes a turbulence producer with a plurality of diffusion tubes in which the diffusion tubes are arranged in rows running across the width of the machine and the separating elements are arranged to begin between the rows of diffusion tubes.
In a headbox provided for a gap former, the upper and lower walls of the headbox can be and, preferably should be, made equal in length.
In accordance with features of the instant invention, it is contemplated that the individual elements can be utilized in various combinations without departing from the scope of the invention.
Accordingly, the present invention is directed to a headbox of a paper machine that includes at least one material suspension supplying system, and a headbox nozzle that includes a first dividing wall having a machine width and a second dividing wall having a machine width, The first and second dividing walls are arranged to form a first path in which a total nozzle cross-section steadily and continually decreases in a material flow direction and to form a second path, arranged to follow the first path, in which a total nozzle cross-section continually increases in the material flow direction.
According to a feature of the instant invention, the first and second walls can be further arranged to form a third path in which a total nozzle cross-section steadily and continually decreases. The third path can be positioned to follow the second path. Further, a length L3 of the third path is shorter than a length L2 of the second path, and the length L2 is shorter than a length L1 of the first path. Moreover, the lengths L1, L2, and L3 conform to the following relationships:
L2xc2x70.3 less than L3 less than L2xc2x70.7; and
L1xc2x70.1 less than L2 less than L1xc2x70.3.
In accordance with another feature of the instant invention, a turbulence producing region can be provided, and the first path may be arranged immediately after the turbulence producing region.
According to still another feature of the invention, the total cross-sectional area of at least one of the first path and the second path forms a single suspension conduit.
The headbox may also include at least one separating element, having a machine width, arranged between the first dividing wall and the second dividing wall. In this manner, a total cross-sectional area of at least one of the first path and the second path includes a plurality of suspension conduits formed by the at least one separating element, the first dividing wall, and the second dividing wall. Further, each of the plurality of suspension conduits within a same path can have a same cross-sectional progression. Additionally, or alternatively, each of the plurality of suspension conduits can have a congruent shape.
According to a further feature of the present invention, the at least one separating element can be located within a region of the second path, and a degree of divergence for each of the plurality of suspension conduits within the second path can be the same. Further still, the at least one separating element can have a pointed end which extends into a region of the second path. The at least one separating element can include a plurality of separating elements, and the pointed ends of each of the plurality of separating elements can include surfaces having a same degree of convergence. A progression of at least one of the upper wall and the lower wall in at least the second region can be symmetrical to a progression of a surface of the separating element adjacent one of the upper wall and the lower wall. A turbulence producer having a plurality of diffusion tubes can also be provided. The diffusion tubes may be arranged in rows extending cross-wise to the run direction, and the separating elements may be positioned between the rows of diffusion tubes.
According to still another feature of the invention, the upper wall and the lower wall may be equal in length.
In accordance with another feature of the present invention, a contraction ratio xcex94H/xcex94L in a region of the first path can be between approximately 0.30/% and 40%, where the contraction ratio relates to ratio between a change in cross-section height, decreasing in the material flow direction of flow, to a path length. Preferably, the contraction ratio may be between approximately 10% and 30%.
According to still another feature of the invention, a divergence ratio xcex94H/xcex94L in a region of the second path may be between approximately 0.1% and 20%, where the divergence ratio relates to a ratio between a change in cross-section height, increasing in the direction of flow, to a path length. Preferably, the divergence ratio may be between approximately 2% and 12%.
According to still another feature of the invention, a contraction ratio xcex94H/xcex94L in a region of the third path is between approximately 1% and 400%, where the contraction ratio relates to a ratio between a change in cross-section height, decreasing in the direction of flow, to a path length. Preferably, the convergence ratio may be between approximately 10% and 200%.
Moreover, according to another feature of the present invention, the first path may be between approximately 250 mm and 1000 mm long, and preferably between approximately 400 mm and 800 mm long. The second path may be between approximately 20 mm and 150 mm long.
The first and second walls may be further arranged to form a third path in which a total nozzle cross-section steadily and continually decreases, and the third path may be positioned to follow the second path. The third path can be between approximately 0.5 mm and 300 mm long, and preferably between approximately 1 mm and 100 mm long.
According to a fiber feature of the instant invention, a smallest total cross-section height of the first path can be between approximately 10 mm and 500 mm, and preferably between approximately 15 mm and 150 mm.
In accordance with a further feature of the present invention, a greatest total cross-section height of the second path may be between approximately 30 mm to 600 mm.
According to a still further feature of the instant invention, the first and second walls may be Her arranged to form a third path in which a total nozzle cross-section steadily and continually decreases, and the third path may be positioned to follow the second path. A smallest total cross-section height of the third path can be between approximately 5 num and 80 mm.
In accordance with another feature of the invention, a region for producing turbulence can be provided. Further, the second path may be shorter than the first path, and second path can be arranged to directly follow the first path and to extend to an end of the headbox nozzle.
According to another feature of the instant invention, the first and second walls may be further arranged to form a third path in which a total nozzle cross-section steadily and continually decreases, and the third path may be positioned to follow the second path. The third path may be arranged to directly follow the second path and to extend to an end of the headbox nozzle,
The present invention is also directed to a process of supplying a material suspension to an output of an apparatus including at least one material suspension supplying system and a headbox nozzle having a first dividing wall with a machine width and and a second dividing wall with a machine width. The process includes accelerating the material suspension along a first path having a total nozzle cross-section that steadily and continually decreases in a material flow direction, and decelerating the material suspension along a second path having a total nozzle cross-section that continually increases in the material flow direction. The second path is arranged to follow the first path.
According to a feature of the present invention, the process may further include accelerating the material suspension along a third path having a total nozzle cross-section that steadily and continually decreases, The third path may be arranged to follow the second path.
According to another feature of the instant invention, the process may further include creating turbulence in the material suspension before being accelerated in the first path.
In accordance with still another feature of the invention, the apparatus may further include a plurality of suspension conduits formed by at least one separating element, having a machine width, being arranged between the first dividing wall and the second dividing wall, and the process may further include at least one of (1) accelerating a plurality of portions of the material suspension through the plurality of suspension conduits in a region of the first path, and (2) decelerating a plurality of portions of the material suspension through the plurality of suspension conduits in a region of the second path. The apparatus can further include a turbulence producer having a plurality of diffusion tubes, and tie process may farther include each row of diffusion tubes producing turbulence in a respective suspension conduit adjacent thereto.
The present invention is also directed to a headbox of a paper machine that includes at least one material suspension supplying system, and a headbox nozzle including a first dividing wall having a machine width and and a second dividing wall having a machine width. The first and second dividing walls are arranged to form a first path in which a total nozzle cross-section steadily and continually decreases in a material flow direction and to form a second path, arranged to follow the first path, in which a total nozzle cross-section continually increases in the material flow direction. The second path directly follows the first path and is shorter than the first path.
According to a feature of the invention, the second path may extend from the first path to an end of the headbox nozzle.
In accordance with another feature of the instant invention, the first and second walls may be further arranged to form a third path in which a total nozzle cross-section steadily and continually decreases, and the third path may be positioned to directly follow the second path.
A turbulence producing region may also be included, and the first path may be arranged immediately after the turbulence producing region.
According to yet another feature of the invention, at least one separating element, having a machine width, may be arranged between the first dividing wall and the second dividing wall. A total cross-sectional area of at least one of the first path and the second path may include a plurality of suspension conduits formed by the at least one separating element, the first dividing wall, and the second dividing wall. The at least one separating element may continuously extend from a region of the first path to a region of the second path.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.